The invention relates to an organometallic electrolyte for the electrodeposition of aluminum as well as to the use of this electrolyte.
For the electrodeposition of aluminum, organometallic electrolytes, i.e., organo-aluminum complex compounds can be used (see German Patent No. 1 047 450: column 9, lines 17 to 31). A number of compounds have been described which can be used for electroplating aluminum, for instance, onium and alkali-complex compounds. In practice the complex salt NaF.2Al(C.sub.2 H.sub.5).sub.3 which is described as the most appropriate, has been used exclusively.
Electroplating baths with NaF.2Al(C.sub.2 H.sub.5).sub.3 as the electrolyte salt, however, have a decisive disadvantage for a technically broad and economical application: the throwing power, i.e., the ability of an electroplating solution to deposit metal uniformly on an irregularly shaped cathode or surface, is too low. It is comparable to that of aqueous chromium baths. Due to the low throwing power in electrodepositing aluminum, parts having a highly irregular profile can only be plated as rack-supported articles, where the geometry of the parts allows through the use of auxiliary anodes. However, this is a technically very painstaking and therefore expensive procedure. Because of the low throwing power of aluminum electroplating baths, barrel aluminum plating of small parts is also not practical, since the aluminum plated parts exhibit excessive layer thickness variations or are not plated at all at critical points.
It is an object of the invention, therefore, to discover an organometallic electrolyte for electrodepositing aluminum which has high throwing power but shows high conductivity and good solubility, and is readily accessible commercially.